Computer Science 432 Operating Systems Williams College Fall 2006

Agenda

• Announcements
  • Computer Science registration open house: Wednesday 11/1, 6 PM
• Term project out
• Lecture assignment recap
• Memory management
  • Contiguous allocation
    • hardware support: limit and base/relocation registers
    • first-fit/best-fit/worst-fit
  • Fragmentation
    • external: waste between allocated chunks
    • internal: waste within allocated chunks
    • reduce external fragmentation with a compaction operation
  • Paging
    • break up logical memory into pages, physical memory into frames
    • page size: the size of these pages/frames
    • can allow virtual memory
    • translate addresses by looking up a frame number using the page number, which is part of the logical address
    • store the translations in a page table in memory
    • a memory access now requires a page table access then the memory access - slow!
    • help: translation lookaside buffer - associative memory that stores a subset of table entries
    • TLBs are small, but locality helps it to have an excellent hit rate in practice
    • page table too large? page it - multilevel page tables
    • another option: inverted page tables
    • memory protection with paging: valid/invalid bits
    • shared pages

Lecture Assignment

Due at the start of class, Thursday, November 2.

Turn in a short answer to question 8.9 in SG&G. Please turn in a hard copy (typeset or handwritten are OK). We will discuss the question during class, so no late submissions are accepted.

The readings for next time are the handout from McKusick, et al.